This application relates to a method for evaluating data received from scanning a circular bar code label.
Bar code labels are utilized in a variety of applications to provide numerical identification, typically about an item carrying the label. A bar code consists of a series of alternate spaces, or light elements, and bars, or dark elements, with the light and dark elements being comprised of a series of wide and narrow elements. In the past, these elements have been positioned extending along a linear direction. A start code pattern is embedded at one end of the bar code label comprised of a known series of elements, and a stop code pattern is formed at the other end. Further, a wide "quiet zone" is formed at each end of the bar code label. The quiet zones and the start/stop patterns allow the scanner system to determine the starting and ending points of the label, and determine when to begin to evaluate the information read from the label and when to stop.
While bar code labels enjoy great success and wide application, certain deficiencies exist in their use. First, the analog readings from a bar code scanner are not constant, even during a single scanning of a single bar code label. Many variables affect the analog signal from the bar code scanner. Thus the analog signal for several dark elements, as an example, within a single scan of a bar code may have widely varying peak values. The signal level can vary from element to element as the contrast on the label changes, or as the angle of the back scattering from the label varies.
The above variation presents a problem when converting the analog information into digital information. This conversion requires a precise determination of the width of the code elements which are made up of bars and spaces. To make this determination, the system must identify the transitions between the dark and light elements, and switch the digital signal when a transition occurs. Typically, a reference voltage is set to identify a transition. Because of the above described variation, however, a fixed threshold or an averaging variable threshold circuit has not been found to be reliable to identify the transitions. Neither type circuit can track nor predict the amplitude of the next transition to be switched between the dark and light elements, or vice versa.
Further, while linear bar code labels provide a very efficient method of reporting data relative to a member which carries the label, they have certain limitations in that they require a relatively large amount of space. Certain applications do not have sufficient space, and thus have not been able to successfully use bar code technology. As an example, small circular elements such as medical test tubes, and sample vials have not been readily adapted to the use of linear bar code labels. Moreover, when a linear bar code label is placed on a curved structure, such as a test tube, other problems are presented in that the starting point for the label, and its relative position to a reader, must be carefully controlled to provide accurate results from the scanning of that label. The label must be positioned such that the beam passes through each element on the label, and this has been difficult to achieve with a linear label on a curved surface.